Prior to the Revival (more accurately Reform) popularized as Wica/Wicca... and the counter-revival popularized by Reconstructionists who throw the baby out with the bathwater... we survived in Europe just as our Afro-diasporic kin survived in the Carribean. In other words, we hid under Mary's skirts, adopting a veneer...
It's more complicated than that. Christianity became the State Cult with Constantine et al. The sacrament of the Mass fulfilled the function as the exoteric sacrifices to the Olympians i.e. generating good will to/from deity on behalf of the community. Personal piety, household worship, and the Mystery cults always referred back or were somehow influenced by the State Cult..
Which is why many Traditionalist Witches and Pagans maintained (some still do) a dual-faith allegiance per se. In Ireland, it is perfectly common to see the Witches/fairy doctors/cunning folk dancing around a bonfire on Saturday night and making offerings to the Sidhe (in all senses of that term), while being at Church the next day...
In Italian Craft, our Deities are masked by the Catholic saints... but the Saints are also recognized as being powerful entities in their own right. Then again, the cult of the Saints is IDENTICAL to the cult of Heroes, down to the keeping of relics and petitions for intercession (often tied to a 9 day feast i.e. root of the novena). Select Saints are known to be "Witch Saints" either because in life they were themselves dual-faith practitioners (and lore states this was common in order to warn the Old Faith adherents of the Inquisition) and/or because they "work with both hands" in response to petitions.
For us, this Catholic veneer per se is a point of cultural pride. It honors our ancestors and preserves something that contributed to our survival. .
Then again, this veneer also explains why certain Deities may be masked by the demons of Christian belief i.e. they were a threat, they were dangerous, and yet... the common people loved them. In Brazil's Quimbanda, we see this with Exu and Pomba Gira (identified with various devils and Goetic djinn). A European/American counterpart exists in occasionally referring to the Horned Master of the Art as "the devil"... but I digress.
A literary example of this dual faith can be found in Harvest Home by Thomas Tyron - a novel which has influenced the Revival in many ways, as well as the novella The Horned Shepherd.
copyright 2015 Jonathan Sousa. Used here with author's permission.
Jonathan Sousa is a Priest of Diana, Stregone, and Benedetto.